A new in-line type tunable liquid crystal fiber-optic device is presented. The main idea is to obtain anisotropic waveguide structure based on biconically tapered isotropic fiber core and anisotropic liquid fiber clad. As the liquid-crystal line clad, the nematic mixture 1110-10C(3) made by Dabrowski's group has been used. The special construction of a device with square cross-section secures a possibility to change molecular orientation of the liquid-crystalline clad by external field. Thus, different polarising action has been obtained depending on fulfilment waveguide condition of the structure.